Estimation of surface-acoustic-wave attenuation due to platelet defects

Surface-acoustic-wave (SAW) attenuation due to platelet defects in quartz substrate (40° rotated Y cut) was investigated. The dimensions of the defects, which are formed in a lapping and polishing process, were quantitatively measured. The data was used in the analytical calculation. SAW attenuation loss in propagating on damaged substrate with deep defects was experimentally measured in the 150–400-MHz frequency range. The loss was obtained from the measured Q value of an IDT resonator, comprising the substrate. By comparing the Q value of the resonator using damaged substrate with that using undamaged substrate, the loss caused by the defects was discriminated from other losses. Steg’s scattering theory was applied to the SAW device and the calculated attenuation loss agreed well with the measured one. The theory also predicts that the attenuation constant in conventionally polished substrate, which contains about 2×104 cracks/cm2 microcracks, is about 1 dB/cm at 1 GHz.